Insulating materials are multicomponent systems whose structure is known to be composed of solid particles and gas volumes. Due to the favorable design and arrangement of these components in the cross section, the insulating effect is generated by small gas occlusions. It is known that the effective thermal conductivity of a material consists of the heat conduction of the solid matter and the effective thermal conductivity of the occluded gas. This results from the shares of the apparent thermal conductivities caused by convection and radiation within the structure and the proper thermal conductivity of the gas.
It is known that the superinsulating materials can be constructed as a layer structure. The layers are formed by thin metal plates--mostly steel--or aluminum plates or by metallized sheets. To prevent the layers from contacting one another, there are inserted spacers which are more or less insulating. These structures can be evacuated if certain demands are met.
Vacuum insulations are mostly used as panels or components, less as large-area materials, since the labor and material expenditure is very high in the course of production.
From DE-OS 39 00 311 A1 there is known a multilayered evacuated structure. Several thin steel sheets are permanently connected with each other by supports with low thermal conductivity using a suitable adhesive. By placing thin fibres or foamed plastic in the space, the radiation losses are reduced. By the position of the fibres parallel to the steel sheets, large contact surfaces are created which increase the thermal bridges and raise the heat losses. Plastic materials or steel are used as supports. Disadvantages of this structure are its stiffness, i.e. no flexibility, and its high weight.
In DE-OS 40 03 770 A1 a heat-insulating encasement for a technical plant is shown. By profiling the aluminum foils, (i.e., forming a cross-section of the aluminum foils into a non-planar shape, which is similar and comparable to corrugating or stamping), the aluminum foils form heat-insulating pockets. In the heat-insulating mat according to DE-OS 35 07 323, metal-coated sheets are directly connected with each other by short weld seams. In the spaces, there are inserted expanding elements which are required for the insulating effect. A disadvantage of these inventions is that a direct contact between the individual sheets is created. This promotes the heat conduction within the foils. These structures are hard and not flexible. Relatively stiff sheets of heavy weight are required for the profiling.
When sheets are used in the structure, the spacing is generated by the filling-in of fibres lying parallel with the sheet by means of ceramic particles or supports of glass-fibre paper. The invention according to DE-OS 35 32 663 A1 describes a soft superinsulation in which links that are incorporated according to a specific geometry provide the spacing of the metallized sheets. In CS 24 30 75 an insulating material is presented in which a non-woven fabric consisting of polyester fibres and/or polypropylene fibres is covered with a metallized sheet. These non-woven fabrics, which are coated with a non-metallized sheet, can be twice doubled and bonded at a specific pressure. This requires great energy expenditure. In all structures, the contact surfaces between the spacers and the sheets are relatively large, because the fibres contact the sheets with their length.
Therefore, heat losses due to heat conduction can be expected.